The proposed research is the first attempt to quantify the professional judgment of industrial hygienists. Professional judgment is the subjective expertise that an industrial hygienist develops as his or her experience sampling air contaminants increases. Many now openly acknowledge that judgment is an essential aspect of the art of practicing industrial hygiene, and it is used informally. As the use of judgment becomes more explicit and formally accepted, research evaluating the reliability of such judgments needs to be performed. Well-established methods from statistical decision theory are available to elicit expert judgments. These methods are used in air pollution, policy analysis, and risk assessment. In the proposed research, expert industurial hygienists will be asked to assess exposures in hypothetical industrial settings. Computer-aided exposure models will be available to the participating industrial hygienists. In some cases, data from small samples of measurements with specified error characteristics will also be available. The experts' predictions will later be compared with the actual levels of exposure in similar industrial settings. Experts will be selected using a panel of well-known industrial hygienists. The industrial sites, for which exposures will be assessed, will be in the Boston area. Conditions of chosen sites will be documented carefully prior to the interviews. Interviews will be conducted at the offices of participating industrial hygienists, and the elicited information will include predictions of exposures in presented scenarios, and the inferred confidence placed by hygienists in specific models for predicting exposures. Results will be presented as calibration curves (accuracy of predictions) with discussion of how the participants used the available exposure models in making predictions.